This invention relates to heat exchangers which regulate the temperature of an integrated circuit via thermal conduction by pressing against the integrated circuit. More particularly, this invention relates to methods and apparatus for use in fabricating a particular type of the above heat exchanger which has a face with an alloy film that presses against the integrated circuit.
In the prior art, U.S. Pat. No. 6,243,944 (hereafter patent ""944) describes an array of several heat exchangers that are held by a frame in alignment with a corresponding array of integrated circuits on a printed circuit board, and each heat exchanger has a face with an alloy film that presses against a respective one of the integrated circuits. See, for example, FIG. 1 in patent ""944 wherein each item 23 is one integrated circuit, and each item 15 is one heat exchanger. See also FIG. 6 in patent ""944 wherein item 15a is the face of one heat exchanger that presses against an integrated circuit, and item 15b is an alloy film on the face 15a.
By providing the alloy film 15b on face 15a of the heat exchanger, the thermal resistance between that face and the integrated circuit is greatly decreased. The alloy film affects the thermal resistance because the face of the heat exchanger, and the surface of the integrated circuit which that face presses against, are not perfectly smooth; and consequently, an irregular shaped microscopic gap exists between the face of the heat exchanger and the integrated circuit. But, when the alloy film on the face of the heat exchanger is melted, the alloy substantially fills the gap; and that causes the thermal resistance to decrease. This is shown in FIGS. 7 and 8 of patent ""944.
The above concept for reducing thermal resistance applies to heat exchangers which have a wide variety of shapes and sizes, and which are held in an array by a wide variety of frames. For example, see U.S. Pat. No. 6,179,047 (hereafter patent ""047) wherein FIG. 1 shows a frame 10 that holds multiple heat exchangers 20 in an array, and each heat exchanger has a face 21 on which an alloy film can be provided. See also, FIG. 10 of patent ""047 which shows another heat exchanger 90 that can be held in an array by the frame 10, and this heat exchanger 90 has a face 91 on which an alloy film can be provided.
However, one problem with the above concept for reducing thermal resistance is how to refurbish the alloy film on the face of the heat exchangers after they have made contact with multiple integrated circuits. This refurbishment is occasionally needed when an array of heat exchangers are held by a frame and are used in equipment which tests many integrated circuits in a sequential fashion. There, when the test on one array of integrated circuits is complete, the heat exchangers are moved to another array of integrated circuits. After about one-thousand to three-thousand arrays of the integrated circuits have been tested, the alloy film on the face of the heat exchangers needs to be refurbished because the alloy film oxidizes and that changes its thermal characteristics.
If the alloy film is refurbished on the face of the heat exchangers while they are held by the frame, then various components which couple the heat exchanger to the frame can become contaminated by various fluids used in the refurbishment process. For example, FIG. 2 of patent ""944 shows that to fabricate the alloy film, a flux must first be spread on the face of the heat exchanger. This flux promotes metallurgical bonding between the face of the heat exchanger and the metal alloy which is subsequently applied as shown in FIGS. 3 and 4. However, if a portion of the flux drips off the face of the heat exchanger, that flux could corrode other components such as the coil springs 20 in FIG. 1 of patent ""944, the leaf springs 30a-30d in FIG. 1 of patent ""047, and the leaf spring 80 in FIG. 10 of patent ""047.
Alternatively, all of the heat exchangers can be removed from the frame before the alloy film is refurbished; and then all of the heat exchangers can be re-attached to the frame. However, the removing step and re-attaching step are time-consuming; and that adds to the cost of the refurbished process.
Also, another problem with the above concept for reducing thermal resistance is how to fabricate the alloy film such that it has a thickness which lies within a narrow preferred range. If the alloy film is too thin, then the irregular-shaped microscopic gap between the integrated circuit and the face of the heat exchanger will not be filled with alloy; and, that will increase the thermal resistance. Conversely, if the alloy film is too thick, then a portion of the alloy could get squeezed off of the heat exchange when the face of the heat exchanger is pressed against the integrated circuit; and that could cause a short-circuit in the test equipment. One preferred range for the thickness of the alloy where it is neither too thick or too thin is 75 xcexcm-100 xcexcm.
In FIG. 3 of patent ""044, the thickness of the alloy film is controlled by placing a solid piece of alloy, of predetermined size, on the face of the heat exchanger; melting that alloy; and spreading the melted alloy to form the film. However, the alloy in FIG. 3 of patent ""044 will form a film on the heat exchanger at all locations which are coated with flux. Thus, if some of the flux in FIG. 2 of patent ""044 drips off of the face onto an adjacent region on the side of the heat exchanger, then that region will also be coated with the alloy film. Consequently, the thickness of the alloy film on the face of the heat exchanger will not be in the predetermined range.
Accordingly, a primary object of the present invention is to provide a method and apparatus for solving the above problems.
The present invention, as claimed herein, is a mechanical assembly that is useful in fabricating an alloy film on a face of a heat exchanger for an integrated circuit. This mechanical assembly is comprised of: 1) the above heat exchanger on which the alloy film is to be fabricated, 2) a retainer for a liquid which has a bottom with an opening thru which the heat exchanger extends such that the retainer surrounds the heat exchanger""s face; and, 3) a compliant member, in the opening of the bottom of the retainer around the heat exchanger, which forms a seal for the liquid between the heat exchanger and the retainer.
Using the above assembly, the alloy film is fabricated by dispensing various liquids (such as a liquid flux, liquid alloy, and water) on the heat exchanger""s face in a sequence; and as that occurs, at least a portion of the liquids fall off of the heat exchanger""s face into the retainer. But, the compliant member prevents the liquids that fall into the retainer from leaking onto any other components which hold the heat exchanger on a frame.
Also in one embodiment, the seal around the heat exchanger is adjacent to the heat exchanger""s face. That enables the alloy film to be fabricated with a precisely controlled thickness on the heat exchanger""s face because no liquid flux and no liquid alloy can inadvertently drip onto any region of the heat exchanger adjacent to its face.